Sunscreens can't guarantee protection

CHICAGO - The long, slow days of summer have arrived and with them the temptation to laze on the beach getting a golden tan.

But don't fool yourself; that slapdash coat of sunscreen isn't a sure safeguard against sunburn or its dangerous relative, skin cancer.

The more you expose yourself to the sun, the higher the risk from potentially harmful ultraviolet radiation, even when you slather on oily creams or chemical-smelling sprays.

Or, as a May research review in the British medical journal The Lancet suggests, "Wearing sun-protective clothes and a hat and reducing sun exposure to a minimum should be preferred to sunscreens."

Consumers' unreliability is a big part of the problem. Being hasty or indifferent, people typically apply too little sunscreen, spread it unevenly or avoid it altogether, noted Dr. Stephan Lautenschalger, a Swiss dermatologist and author of the review.

That helps explain recent data from the Centers for Disease Control and Prevention demonstrating that more adults in the United States are getting sunburns _ 33.7 percent in 2004, up from 31.8 percent in 1999.

Being darker-skinned didn't eliminate the risk: Substantial numbers of Hispanics, Asians and American Indians scorched in the sun, according to the CDC report. African-Americans also are affected, depending on their skin color and family history of skin cancer, it noted.

At a minimum, people should put on a "shot-glass full" of sunscreen before they go out and reapply the same amount every few hours, said Dr. Carolyn Jacob, a Chicago dermatologist. Few do.

Instead, many sunscreen users put themselves at heightened risk by spending extra hours in the sun, falsely assuming they're safe from harm, according to the Lancet review.

Products that promise they are "waterproof" or they will "block" ultraviolet rays feed an illusion of almost total protection. But both claims are unfounded: No sunscreen blocks all UV radiation or will stay on all day as people swim, sweat and towel themselves off after exercise, Jacob said.

In fact, the sunscreens you grew up using _ those creams you rubbed in before jumping in the waves _ did nothing more than shield you against ultraviolet B radiation (UVB), which is responsible for burns that turn people tomato-red, then blister.

For years, it was believed UVB was the primary culprit in skin cancer. Prevent the burns and reduce UVB exposure and you'll get less cancer, experts reasoned.

In this vein, the sunscreens' sun protection factor (SPF) rating measures only the degree to which a product filters out UVB. When applied adequately, a SPF-15 sunscreen offers 93 percent protection from UVB, compared with 98 percent for SPF-50.

Left out of the equation was wrinkle-inducing ultraviolet A radiation (UVA), longer waves that penetrate the skin more deeply. Over the past decade research has accumulated demonstrating that UVA exposure contributes to skin cancer as well.

Industry has adapted by developing "broad spectrum" sunscreen products containing UVA-blocking ingredients such as avobenzone, oxybenzone, mexoryl, zinc oxide and titanium oxide. But the Food and Drug Administration still hasn't come out with a system for rating UVA protection, leaving consumers uncertain how to evaluate products' benefits.

"We're working on it, and we hope the proposed industry guidance will be out this summer," said Sandy Walsh, an FDA spokeswoman.

As for the science behind sunscreens and skin cancer, it's mixed.

Dr. David Leffell, professor of dermatology and surgery at Yale School of Medicine, explained that there is good evidence of efficacy for basal cell carcinoma and squamous cell carcinoma, the two most common types of skin cancer.

In both cases, ultraviolet radiation causes "mutations" in skin cells that "disable" a gene whose job is "to suppress the development of skin cancer," Leffell said.

Four years ago, a study in the prestigious New England Journal of Medicine proved that daily use of sunscreen reduced the number of new pre-cancerous cells in people deemed at high risk of skin cancer. The findings applied to squamous cell carcinoma and are thought to extend to basal cell carcinoma as well.

But melanoma, the most deadly type of skin cancer, is "a different entity," Leffell noted. Some melanomas are clearly related to sun exposure; others aren't.

Some epidemiological studies indicate that sunscreen helps reduce the rate of melanoma; other studies don't.

In 2000, a panel of the World Health Organization concluded that there was insufficient evidence establishing the efficacy of sunscreen in preventing melanoma. "There weren't human studies," a problem that persists to this day, said Dr. June Robinson, a Northwestern University dermatologist who sat on the panel.

Still, Robinson believes there is reason for confidence in sunscreens. "We know that cancers are caused in animal models by UV light. We know sunscreen blocks UV light. It's a reasonable, logical step to believe that prevents the development of all three forms of skin cancer," she said.